The imagery of Pentecost may be important. Pentecost is a pilgrim-holiday also known as the Feast of Weeks or Shavuot. The holiday celebrated the Firstfruits of the harvest. The Festival of Weeks was the smallest of the three pilgrim festivals, falling 50 days after Passover (seven weeks), the late spring / early summer. This festival was an offering of two loaves made with the new wheat given in the firstfruit offering.
The point of the festival was “to declare God’s ownership of the land and his grace in bringing forth food. According to a tradition found in the book of Jubilees, Pentecost was the day on which Moses was given the Law (cf. Tob 2:1, 2 Mac 12:32). This tradition is based on the belief that the Israelites arrived at Sinai 50 days after the first Passover (Exod 19:1). Some scholars (Knox, Snaith) have made a connection between this tradition and the gift of the Holy Spirit (ie., Moses gave out the Law to Israel on this day, Jesus gives the Holy Spirit to the church). Fitzmyer thinks Luke was aware of the tradition since there are some indirect allusions to the giving of the Law in Acts 2, not the least of which is the image of fire descending (Exod 19:18).
It is at least possible to see the idea of “firstfruits” applied to the Holy Spirit. The new age has begun and the Holy Spirit has come for the first time. But we also need to consider two other potential “Pentecosts” in the book of Acts. In Acts 10 the Holy Spirit falls on Cornelius, a God-Fearing Gentile, and he speaks in tongues just like Pentecost. Peter makes this point clear in Acts 10:47, the Gentiles in Cornelius’ home received the Holy Spirit “just as we have.”
But there is a third reference to Pentecost in Acts 20:16. Paul is adamant that he reach Jerusalem before Pentecost if possible. This return to Jerusalem was dangerous, but Paul wanted to deliver the Collection from the Gentile churches at Pentecost if at all possible. Why? Because the sharing of gifts from the Gentile churches indicates that they too have received the Holy Spirit. Paul’s return to Jerusalem at Pentecost is calculated to highlight his “harvest” among the Gentiles. Three references to Pentecost is not unexpected since there are other repetitions of events on Acts (Cornelius’ conversion, Paul’s conversion, the rejection of Israel, etc.)
Whatever the intended imagery, the day represents the largest crowd in the Temple area after Passover. Peter and the other apostles are able to preach to large crowds of biblically-minded Jews gathered to worship God in the Temple (Acts 2-3). Is there anything in Peter’s sermon that makes some use of this Pentecost imagery? In other words, why is Pentecost the time God chose for the outpouring of the Spirit?
Bibliography: W. L. Knox, Acts, (NCB, Oxford: Clarendon, 1967), 80-84; N. Snaith, “Pentecost, the Day of Power,” ExpTim 43 (1931-32): 379-80.